Heretofore centrifugal pumps could successfully be used in the paper and cellulose industry only for pumping fiber suspensions or pulps having consistencies less than 6% provided the pump has been correctly designed and its input pressure is adequately high. A centrifugal pump was not, however, suitable for high consistency pulps because due to flocculation of the pulp, the pump has a tendency to become clogged. Expensive pumps based on the displacement principle must therefore be used for pumping high-consistency pulps.
It should be stressed that in a fiber suspension of consistency above 6%, the fibers tend to form flocs which interlock to form a coherent network which goes through a pipe like a solid, giving plug flow. Most experiments with high consistency pulps have been carried out in an effort to achieve a high degree of agitation and turbulence so that air bubbles are prevented from building up ahead of the impeller inlet. Undoubtedly, this gives some advantages, but agitation requires high energy expenditure.
It is an object of the invention to provide a method and an apparatus for pumping pulps of considerably higher consistencies than heretofore possible by using centrifugal pumps.
Another object of the present invention is to subject the pulp suspension to such shear forces that fluidization is achieved.